Moving armature receivers are widely used to convert electrical audio signals into sound in portable communication applications such as hearing instruments, headsets, in-ear-monitors, earphones etc. Moving armature receivers convert the electrical audio signal to sound pressure or acoustic energy through a motor assembly having a movable armature. The armature typically has a displaceable end or region that is free to move while another portion is fixed to a housing or magnet support of the moving armature receiver. The motor assembly includes a drive coil and one or more permanent magnets, both capable of magnetically interacting with the armature. The movable armature is typically connected to a diaphragm through a drive rod or pin placed at the deflectable end of the armature. The drive coil is electrically connected to a pair of externally accessible drive terminals positioned on a housing of the miniature moving armature receiver. When the electrical audio signal is applied to the drive coil the armature is magnetized in accordance with the audio signal. Interaction of the magnetized armature and a magnetic field created by the permanent magnets causes the displaceable end of the armature to vibrate. This vibration is converted into corresponding vibration of the diaphragm due to the coupling between the deflectable end of the armature and the diaphragm so as to produce the sound pressure. The generated sound pressure is typically transmitted to the surround environment through an appropriately shaped sound port or spout attached to the housing or casing of the movable armature receiver.
A maximum sound pressure output of a moving armature receiver is created by maximum displacement, or deflection, of the armature as it vibrates. The maximum deflection is set by a maximum magnetic flux carrying capacity of the armature and its mechanical stiffness. A higher magnetic flux means that larger magnetic forces are generated to displace the armature. With increasing mechanical stiffness of the armature, more magnetic flux is needed to displace the armature. The maximum magnetic flux carrying capacity is constrained by material properties of the armature and a cross-sectional area of the armature. The latter property also influences the mechanical stiffness which increases with increasing cross-sectional area. Thus, merely increasing the cross-sectional area of the armature does not provide a significant improvement in the maximum deflection of the armature.
U.S. Pat. No. 7,443,997 discloses an armature for a receiver with a connection portion in communication with first and second leg portions. The connection portion has a width greater than the width of the first and second leg portions individually but a thickness less than the thickness of each of the first and second leg portions to reduce the stiffness of the armature.
The present invention is based on a multi-layer construction of the armature where adjacently arranged armature layers are at least partly magnetically coupled to each other while allowing relative mechanical displacement over at least a segment or portion of the armature layers. This multi-layer construction creates considerable design freedom in choosing armature geometry outside the bounds posed by the above-mentioned conventional constraint between armature cross-sectional area and mechanical stiffness. The design freedom can be applied to create numerous performance benefits for the moving armature receiver such as higher electroacoustic conversion efficiency, increased maximum sound pressure output or decreased length of the armature and thus size of the moving armature receiver.